Our invention relates to a process for determining and controlling fuel mass flow in the partial oxidation and gasification of fine-grained to powdery fuel.
Our process determines and controls fuel mass flow, which is supplied to a gasifying unit with at least two burners in the partial oxidation and gasification of a fine-grained to powdery fuel, using a radiometric density measurement of the fuel transported from a central supply vessel to the individual burners by a gaseous medium and using a process computer for performing the required computational operations.
In gasification of solid combustible materials, such as brown coal or soft coal and/or oil coke, the fine-grained to powdery combustible material, which if necessary can be brought to the desired grain size by a grinding process, must be fed to the gasification unit with the gaseous and/or vaporous reaction medium in a uniform and quantitative accurate flow. This is required, so that constant operating conditions can be set in the gasification unit, by which a uniform quality and quantity of partially oxidized gases produced is guaranteed. Oxygen and air and/or air enriched with oxygen and if necessary added water vapor can be used as the gaseous and/or vaporous reaction medium. If the fuel components in the reaction mixture are too small in the gasification unit, an undesirable increase of the operating temperature in the gasification unit is caused because of the high oxygen:fuel ratio. If in contrast the reverse is true and the fuel components in the reaction mixture in the gasification unit are too high, this causes an incomplete reaction of the fuel with the oxidizing agent. It is thus possible that unconverted fuel particles are deposited in the gasification unit or are carried out together with the gas produced from the gasification unit. Furthermore under these circumstances the reaction can then halt or be interrupted. Variations of the fuel mass flow fed to the gasification unit lead necessarily to variations in the flow of partially oxidized gases produced, which naturally can also impair the subsequent consumption of the gas. That is particularly the case, when the partial oxidized gas is produced for combustion in a gas turbine in a gas and steam turbine power plant connected to the gasification unit. Here in the interest of a uniform and trouble-free operation of the power plant it must be unconditionally guaranteed that the combustion gas flow required for gas turbine operation must be available in a sufficient extent and also on shutting down or reducing the operation of the gas turbine the combustion gas feed and thus the gasification output can be choked or reduced as quickly as possible and without difficulty.
Because of the above-named reasons it is necessary to determine and control as accurately as possible the the fuel mass flow, which is fed to the individual burners of the gasification unit. Because of that the modern gasification units today are equipped continuously with at least two burners distributed uniformly about the periphery of the reactor, which must be simultaneously provided with fuel.
In the German Published Patent Application No. 33 16 368 a process for determination and observation of the fuel mass flow supplied to the gasification unit was set forth in which each burner of the gasification unit is connected by a separate pipe with the central supply vessel for the fuel feed. In each of these pipes the fuel flow conveyed with the fluidizing gas is subjected to a radiometric density measurement and subsequent to that a pressure difference measurement. From the value obtained together with the value for the fluidizing gas fed to the supply vessel and the fluidizing gas conducted away from it the fuel mass flow is determined in a process computer.
Previously described processes limit themselves to the determination and observation of the fuel mass flow, which is fed to the individual burners of the gasification unit. In contrast nothing is expressed about control of this mass flow in these previous processes. Furthermore the processes previously described are also expensive in regard to apparatus, since in each of the pipes leading to the individual burners of the gasification unit a radiometric density measurement must be performed.